Online harassment is often ignored or belittled. It's dismissed as 'harmless fantasy'. The fact of its persistence is often ignored; that persistence, rather than being seen as a disturbing indicator of a twisted psyche, is seen as annoying, rather than threatening.
I've not, generally, been harassed, either in person, or online. But, this woman's experience is beyond creepy. That a supposedly grown man would stoop to such a level should cause concern.
Understand, I'm not in favor of clamping down on EVERY rude, obscene, or vaguely hostile comment. But, when that person crosses the line - threatens real-life attacks, continues that hostility for years, is not a kid - yeah, get the legal system involved, and issue a restraining order. When that order expires, if the person continues the practice, make it permanent.